Apparatus for cooling electronic components within a computer system enclosure

ABSTRACT

A heat generating component such as a microprocessor, in a small form factor, low profile electronic device such as a laptop computer is cooled by using an elongated hollow heat exchanger with a fan at one end of the heat exchanger. A heat pipe, having two ends, has one end thermally coupled to the heat exchanger and the other end thermally coupled to the heat generating component. A heat sink thermally coupled to the other end of the heat pipe, in thermal contact with the heat producing component may be used. In a laptop computer having a four vertically extending side walls including a front wall a back wall and two side walls where the heat generating component is a microprocessor, the heat exchanger can extends in a direction adjacent and parallel to one of the side walls, with an air outlet formed in one of said front and rear walls and an air inlet in the other of said front or rear walls or the side wall to which the heat exchanger is adjacent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part application of pending prior applicationSer. No. 08/723,905 entitled “A FAN BASED HEAT EXCHANGER” filed on Sep.30, 1996.

FIELD OF THE INVENTION

The present invention relates to the cooling of electronic componentswhich generate high amounts of heat in general and more particularly toa method and apparatus for removing heat from an electronic heatgenerating component in an electronic system having a small form factor.

BACKGROUND OF THE INVENTION

A number of present day electronic components utilized, for example, incomputer systems, generate large amounts of heat. These components, suchas microprocessors and associated components are typically encapsulatedin plastic or ceramic from which a plurality of leads extend. Theintegrated circuit (IC) is mounted to a printed circuit board either bydirect soldering or through a connector which is soldered to the printedcircuit board. In a typical personal computer system, a processor, whichin most cases in current systems is a high speed processor whichgenerates a great deal of heat, is mounted on a printed circuit boardknown as a motherboard, along with a plurality of other components thatsupport the processor such as memory circuits. Also contained within thepersonal computer housing are additional circuits or circuit boards suchas video cards, facsimile-modem cards, etc. The housing may also containa power supply, supplying power to all of the various components.

As explained in co-pending application Ser. No. 08/686,856, filed May31, 1996 and assigned to the same assignee as the present invention, thedisclosure of which is hereby incorporated by reference in its entirety,it is desirable to have a high rate of heat transfer from the IC packagein order to maintain junction temperatures within the IC inside safeoperating limits. As noted, modern microprocessors typically employmillions of transistors in internal circuitry that requires some type ofcooling mechanism to avoid excessive junction temperatures that mayeffect the performance of the circuit and can cause permanentdegradation of the device. As noted in that application, this is aparticularly difficult problem in the design of computer systemenclosures which have a small form factor such as laptop and notebookcomputers. However, heat removal also can constitute a problem in othertypes of systems which have high power profile components located withina small form factor or thin profile electronic device.

Aside from the possibility of affecting the performance of the circuitsin the IC and degradation of those circuits, high heat generatingcomponents which are located within consumer electronic devices, such aslaptop computers, can create hot spots at certain locations along theexternal casing of the devices. These hot spots can be uncomfortable totouch and may even cause burns. This is a further reason for conductingheat away from these hot spots and cooling the components generatingthem to avoid injury to users.

The aforementioned application describes prior art methods used toremove heat from heat generating components located within the confinesof a computer enclosure, which include the simple attachment offinned-heat sinks; the development of finned-heat sinks with intricatefins; the use of large flat heat spreading plates to which an IC isdirectly or indirectly attached; and the thermal coupling of theintegrated circuit to a heat spreading plate by a heat pipe or other lowresistance thermal path. As described, more recently, forced cooling airhas been used to cool one side of a heat spreading plate having anintegrated circuit attached to the other side. The prior applicationrecognizes that these prior art methods do not provide sufficient heatremoval capacity and/or efficiency needed to cool current and futurehigh performance microprocessors and other high heat generating devicesin portable general purpose or other thin profile electronic devices.

The solution proposed in that application is the use of an air ductcomprising a thermally conductive housing having internal fins dispersedalong the internal walls of the air duct. An airflow generator, e.g., afan, produces an airflow that is directed from an inlet port located ator near the center of the air duct to first and second exit portslocated adjacent opposite ends of the duct. The heat generatingintegrated circuit such as a microprocessor is thermally coupled to thethermally conductive housing by means of a low resistance thermal pathsuch as a heat pipe.

Such an arrangement efficiently removes large amounts of heat. However,the location of the inlet port near the center of the air duct asdescribed in the aforementioned application requires openings above theair inlet in the housing of the device. In the case of a laptop computerthis can cause a problem, since in many current laptop computers, aconvenient place to locate such openings is not available because itwould occur in the area of the keyboard.

Because of this, there is a need for an improved apparatus and method tosolve the problem of cooling high heat generating components such asmicroprocessors within portable consumer electronic and computerdevices, which retain the highly efficient cooling performance of theaforementioned application within the available space, but avoid theproblem of drawing air in through the top surface of the device in orderthat it can be used with a device such as a laptop computer which doesnot have an area on its top surface available for air intake.

SUMMARY OF THE INVENTION

The present invention provides such an apparatus for cooling a heatgenerating component through the use of an elongated hollow heatexchanger with a fan at one end of the heat exchanger. A heat pipe hasone end thermally coupled to the heat exchanger and the other endadapted to be thermally coupled to the heat generating component. Whenused in a small form factor, low profile electronic device such as alaptop computer, the heat generating component, e.g., a microprocessor,is coupled to the heat pipe. In one embodiment, a heat sink is thermallycoupled to the heat pipe, the heat sink being in thermal contact withthe heat generating component. In other embodiments, the heat pipe isattached directly to the heat generating component.

Various embodiments of the present invention are disclosed including onein which one end of the heat pipe is in thermal contact with the outsidesurface of the heat exchanger duct. Preferably there are members, e.g.,fins, attached to the inner surface of the heat exchanger ductincreasing its internal surface area. The heat exchanger duct may have arectangular or cylindrical cross section.

The members on the inside may take various forms such as convolutedfins, plate fins or pin fins. In another embodiment, the heat pipeextends through the center of the hollow heat exchanger duct and aplurality of longitudinal radial fins extend between the heat pipe andthe inside wall of the heat exchanger duct, supporting the heat pipe. Inthe illustrated embodiments, the fan draws air through the heatexchanger duct. It could equally well blow air into the heat 20exchanger duct.

In one embodiment, the heat exchanger extends in a direction adjacentand parallel to one of the side walls of the laptop housing. An airoutlet is formed in the rear wall and an air inlet in the side wall towhich the heat exchanger is adjacent. The fan is disposed between theair outlet and the one end of the heat exchanger. In some embodimentsthere is a curved deflector between the inlet opening and the other endof the heat exchanger and/or an expansion duct between the one end ofthe heat exchanger and the fan.

The arrangement of the present invention allows the use of the verticalwalls as an air inlet and outlet, thus avoiding interference withelements such as a keyboard on the top of the device. In one embodimentthis is done by thermally coupling one end of a heat pipe having twoends, to the heat generating component, such as a microprocessor,thermally coupling the other end of the heat pipe to an elongated hollowheat exchanger and generating a flow of air through the hollow heatexchanger using a fan disposed at one end while drawing air in throughthe other end.

In another embodiment, the condenser portion of the heat pipe isconfigured to include fins to increase the heat transfer area of theheat pipe. In such an embodiment, the heat exchanger includes a housingfor directing an air flow across the heat pipe fins.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the heat exchanger according to thepresent invention in a notebook computer.

FIG. 2 is a plan view of the connection between the heat sink of theheat generating component and the heat exchanger via a heat pipe.

FIGS. 3A and 3B are cross sectional side and front views respectivelythrough the heat exchanger within the housing of the computer.

FIGS. 4A-E illustrate various possible arrangements of the heatexchanger.

FIGS. 5A-5C illustrate a number of possible internal fin arrangementsfor a heat exchanger duct such as the duct of FIG. 4A.

FIG. 6 is a perspective view of another embodiment of the presentinvention.

FIG. 7 is a perspective view of yet another embodiment of the presentinvention.

FIG. 8 is a perspective view of another embodiment of the presentinvention.

FIGS. 9A and 9B illustrate various finned heat pipe and heat exchangerconfigurations.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of the heat exchanger according to thepresent invention. Illustrated is a notebook or laptop computer 11including an enclosure with vertical side walls 27 and 30, a verticalfront wall 32 and a vertical rear wall 34. As is conventional, thelaptop includes a display 13. The laptop is shown with the top of itsenclosure, which would contain the keyboard, removed. Only thecomponents related to the present invention are illustrated inside thelaptop 11. It will, of course, include many additional components, manyof which generate heat. Within the enclosure of the notebook computer 11is a central processing unit 15 which is a high heat generatingcomponent from which heat must be removed to both maintain theperformance of the processor and also to avoid hot spots on the housingof the computer 11. The processor is connected to a heat sink 16 whichin turn is thermally connected to a heat pipe 17. The heat pipe 17 isthermally coupled to an elongated hollow heat exchanger 19 with openingsat its opposed ends. The heat exchanger 19 has an air inlet 21 at oneend and an air outlet 23 at the other end. Air is drawn through the heatexchanger, which has a hollow interior with an increased surface area(e.g., using finned surfaces) by a fan 25. As illustrated, an expansionduct 24 can be provided at the outlet 23 coupling it to the fan 25. Anair inlet 28 is formed in the side wall 27 of the housing 11 of thecomputer. An air outlet opening 29 is formed in the rear wall 34 of thehousing 11 of the computer.

The use of an elongated hollow heat exchanger 19 which has its air inlet21 at one end and air outlet 23 at the other end permits an arrangementin which the air inlet opening 28 and the air outlet opening 29 can bothbe formed in vertical walls such as vertical side wall 27 of the laptop11. Although these openings are shown as being located in the side wall27 and rear wall 34 of the laptop 11, it would, of course, be possibleto locate them in different ones of the vertical walls of the housing ofthe laptop 11. For example, the air inlet could be in the front wall 32and the air outlet in the rear wall 34. Alternatively, the heatexchanger 19 could extend in a direction perpendicular to that in whichit is shown with the air outlet being in the side wall 27 and the airinlet either in the front wall 32 or the side wall 30. In addition, asindicated by an arrow originating at the inlet 28, inside air is drawninto the heat exchanger aiding in the cooling of other components withinthe enclosure of the laptop computer 11. Furthermore, although shown asemployed in a notebook or laptop computer, the present invention canalso be employed with other electronic devices, particularly thosehaving a small form factor with a low profile.

FIG. 2 shows further details concerning an arrangement according to thepresent invention. The heat sink 16 for the CPU 15 of FIG. 1 is inthermal contact with the heat pipe 17 which is bent at a 90° angle. Theheat pipe 17 is in contact with the heat exchanger 19 along one surfacethereof. As illustrated, a deflector 44 can be provided to deflect aircoming in the direction of arrows 43 from the opening 28 into thehousing into the interior of the heat exchanger 19.

FIGS. 3A and 3B are cross sectional side and front views respectivelythrough the heat exchanger 19 within the housing of the computer. As canbe seen from FIG. 3B, in one embodiment the heat exchanger includes aduct 41 with a rectangular cross section. Within the interior of theheat exchanger duct 41 are a plurality of fins 45 to increase thesurface area in contact with the air moving through the duct 41. Theheat pipe 17 is shown in FIG. 3B adjacent to and in thermal contact withthe duct 41 of the heat exchanger 19. In conventional fashion, asdescribed in the aforementioned co-pending application, the heat pipe 17includes a wick 46 and contains a working fluid which is evaporated bythe heat generated at the heat sink 16 associated with the heatgenerating component, i.e., the CPU 15. The vapor is condensed along thesurface of the heat pipe in contact with the heat exchanger 19permitting the condensed fluid to then be wicked back to the heated endof the heat pipe where it is again condensed, forming a close system.FIG. 3A also shows the location of the fan 25 and deflector 44.

FIGS. 4A-E illustrate various possible arrangements of the heatexchanger 19. As illustrated in FIG. 4A, the heat exchanger has a duct41 with a round or rectangular cross section at the outlet end of whichis the expansion duct 24 to which the fan 25 is coupled to draw airthrough the duct 41. The duct 41 has fins 45 on its internal surfacewhich direct the air through an air outlet such as the air outlet 25shown in FIG. 1. Also included is the optional flow turning deflector 44which is useful in the case where the air inlet is in a wall parallel tothe orientation of the heat exchange duct 44 such as the air inletopening 28 shown in FIGS. 1 and 2. FIG. 4B shows a heat exchanger duct41 of cylindrical cross section in which the fan 25 is of the samediameter as the duct 41. Again, the optional flow turning deflector 44at the air inlet is shown.

FIG. 4C shows a heat exchanger duct 41 which has at its outlet a flowturning and expansion duct 47 to which the fan 29 is coupled. There isno flow turning deflector at the air inlet. In this case, with referenceto FIG. 1, the air inlet in the vertical wall of the housing would belocated in the front wall 32 and the air outlet in the sidewall 27. FIG.4D shows a further embodiment similar to that of FIG. 4B with a fan 29of the same size as the duct 41. However, in this embodiment, asillustrated by FIG. 4E, which is a cross sectional view of the heatexchanger of FIG. 4D, a heat pipe 51 is located in the center of theduct 41. The heat pipe is supported by longitudinal radially extendingfins 53.

FIGS. 5A-5C illustrate a number of possible internal fin arrangementsfor a heat exchanger duct such as the duct 41 of FIG. 4A. In each case,the duct is shown as a rectangular duct. Thus, in FIG. 5A within theduct housing 41 of the heat exchanger 19, convoluted fins 61 areprovided. In the embodiment of FIG. 5B plate fins 63 are used and in theembodiment of FIG. 5C pin fins 65 are used. These are given as examplesonly; any type of fin known in the art is usable for this purpose. Thearrangements of FIGS. 5A, B and C can be manufactured using wellestablished techniques, for example, the extrusion of pin or plate finsor brazing of convoluted fins such as in FIG. 5A to the base. In thearrangement of FIG. 5A the convoluted fins are bonded to the rectangularshroud or duct 41.

Turning now to FIG. 6, another embodiment of the present invention isshown. The computer assembly includes an integrated circuit device 80comprising a semiconductor substrate 82. A heat pipe 84 is configured toremove heat away from integrated circuit device 80 and into heatexchanger 19. Heat pipe 84 includes an evaporator portion 86 a and acondenser portion 86 b. Evaporator portion 86 a has a flat heat pipeconfiguration and is attached directly to the semiconductor substrate 82of device 80 by a thermal adhesive. The direct atachment of heat pipe 84to the semiconductor substrate increases the thermal efficiency of theheat removal system by minimizing the thermal resistance between theintegrated circuit device 80 and heat exchanger 19. In the embodiment ofFIG. 6, the evaporator portion 86 a of heat pipe 84 is shaped and sizedto have a surface area that is approximately equal to the surface areaof the semiconductor substrate. It is important to note, however, thatthe present invention is not limited to any particular heat pipeconfiguration. For example, heat pipe 84 may include a flat heat pipeconfiguration, a circular heat pipe configuration, or any of a varietyof other shapes or combination of shapes.

In FIG. 7, an alternative heat exchanger and heat pipe configuration isshown. In the preceding discussion, the condenser portion of the heatpipe was either thermally attached to the outer surface of the heatexchanger or supported within the heat exchanger cavity by a pluralityof longitudinal fins, or other means. In the embodiment of FIG. 7, aheat pipe 90 is provided having an evaporator portion 92 a and acondenser portion 92 b. The evaporator portion 92 a has a flat heat pipeconfiguration and is attached to the semiconductor substrate 82 ofintegrated circuit device 80. In an alternative embodiment, evaporatorportion 92 a includes a circular heat pipe configuration and isthermally coupled to the integrated circuit 80 through a thermallyconductive plate/heatsink 16 as shown in FIG. 8. The condenser portion92 b has a circular heat pipe configuration and has one or more fins 94extending outward from the heat pipe. Fins 94 increase the heat transferarea of condenser portion 92 b, thereby increasing the heat transfercapability of apparatus. Condenser portion 92 b is contained within ahousing 96 which is used to direct a cooling medium, such as air, acrossfins 94.

It is important to understand that the present invention is not limitedto any particular heat pipe or fin configuration. FIGS. 9A and 9Billustrate other possible heat pipe configurations. FIG. 9A illustratesa front view of the condenser portion of a heat pipe 100 having radiallyextending, longitudinal fins 102. Heat pipe 100 is attached to the sidewall of an air duct housing 104. In such an embodiment, housing 104 ispreferrably made of a thermally conductive material, such as aluminum.FIG. 9B illustrate a front view of the condenser portion of a heat pipe110 in yet another embodiment of the present invention. As illustrated,the condenser portion comprises a flat heat pipe configuration havinglongitudinal fins 112 extending outwardly from the heat pipe. Thecondenser portion is contained within a housing 114. The fins may beproduced at the time the heat pipe manufactured by means of an extrusionprocess. Alternatively, the fins may be welded to the outer surface ofthe heat pipe.

Thus, an improved cooling system for a computer system enclosure hasbeen described. Although the present invention has been described withreference to specific exemplary embodiments, it will be evident thatvarious modifications and changes may be made to these embodimentswithout departing from the broader spirit and scope of the invention.Accordingly, the specifications and drawings are to be regarded in anillustrative rather than a restrictive sense.

What is claimed is:
 1. A computer assembly comprising: an integratedcircuit device comprising a semiconductor substrate; a heat exchanger;means for moving a cooling medium through said heat exchanger; and aheat pipe comprising a evaporator portion and a condenser portion, saidevaporator portion being attached to said semiconductor substrate, saidcondenser portion being thermally coupled to said heat exchanger.
 2. Thecomputer system of claim 1 wherein said heat exchanger includes anenclosed duct with an outer surface and an inner surface, said condenserportion of said heat pipe thermally coupled to said outer surface ofsaid enclosed duct.
 3. The computer system of claim 2 further includingmembers attached to said inner surface of said heat exchanger ductincreasing the internal surface area of said heat exchanger.
 4. Thecomputer assembly of claim 3 wherein said members comprise convolutedfins.
 5. The computer assembly of claim 3 wherein said members compriseplate fins.
 6. The computer assembly of claim 3 wherein said memberscomprise pin fins.
 7. The computer assembly of claim 2 wherein saidmeans for moving a cooling medium through said heat exchanger includes afan for directing air through said enclosed duct.
 8. The computerassembly of claim 1 wherein said condenser portion of said heat pipecomprises a circular heat pipe and said evaporator portion of said heatpipe comprises a flat heat pipe.
 9. The computer assembly of claim 8wherein said evaporator portion and said semiconductor substrate havesubstantially the same shape.
 10. The computer assembly of claim 1wherein said semiconductor substrate comprises silicon.
 11. The computerassembly of claim 1 wherein said heat exchanger includes an enclosedduct with inner and outer surfaces and said heat pipe extending throughthe center of said enclosed duct and further including a plurality oflongitudinal radial fins extending between said heat pipe and the innersurface of said enclosed duct, supporting said heat pipe.
 12. A computerassembly comprising: an integrated circuit device comprising asemiconductor substrate; an air duct; air moving means for producing anair flow through said air duct; and a heat pipe comprising a evaporatorportion and a condenser portion, said evaporator portion being attachedto said semiconductor substrate, said condenser portion being attachedto said air duct.
 13. The computer assembly of claim 12 wherein said airmoving means comprises a fan.
 14. The computer assembly of claim 12wherein said condenser portion of said heat pipe comprises a circularheat pipe and said evaporator portion of said heat pipe comprises a flatheat pipe.
 15. The computer assembly of claim 12 wherein saidsemiconductor substrate comprises silicon.
 16. The computer system ofclaim 12 wherein said air duct has an outer surface and an enclosedinner surface, said condenser portion of said heat pipe in thermalcontact with said outer surface of said air duct.
 17. The computerassembly of claim 16 further comprising fins attached to said enclosedinner surface.
 18. The computer assembly of claim 12 wherein said airduct includes an enclosed inner surface and an outer surface and saidcondenser portion of said heat pipe extending through the center of saidair duct and further including a plurality of longitudinal radial finsextending between said heat pipe and said enclosed inner surface of saidair duct.
 19. Apparatus for cooling a heat generating componentcomprising: a heat pipe having an evaporator portion and a condenserportion, said evaporator portion being thermally coupled to said heatgenerating component, said condenser portion having an outer surfacewith at least one fin protruding from said outer surface; and means formoving a cooling medium across fin.
 20. The apparatus of claim 19wherein said heat generating component is an integrated circuitcomprising a semiconductor substrate, said evaporator portion of saidheat pipe being attached to said semiconductor substrate.
 21. Theapparatus of claim 19 wherein said means for moving a cooling mediumincludes a fan for producing an air flow across said fin.
 22. Theapparatus of claim 19 further comprising an enclosed duct surroundingsaid heat pipe and said at least one fin.
 23. The apparatus of claim 22wherein said means for moving a cooling medium includes a fan forproducing an air flow through said enclosed duct.
 24. An apparatuscomprising: a heat generating component; a heat exchanger; a fanpositioned to move air through said heat exchanger; a heat pipe having afirst portion comprising an evaporator portion thermally coupled to saidheat generating component and having a second portion comprising acondenser portion thermally coupled to said heat exchanger.
 25. Theapparatus of claim 24 wherein said heat exchanger is a duct that is anenclosed duct.
 26. The apparatus of claim 25 wherein said duct includesa plurality of fin members.
 27. The apparatus of claim 25 wherein saidsecond portion of said heat pipe is thermally coupled to an outersurface of said duct.
 28. The apparatus of claim 25 wherein said secondportion of said heat pipe is thermally coupled to an inner surface ofsaid duct.
 29. The apparatus of claim 24 wherein said heat generatingcomponent comprises an integrated circuit having a semiconductorsubstrate, and wherein said first portion of said heat pipe is coupledto said semiconductor substrate.